1. Field of the Invention
The present invention generally relates to a filter housing assembly having a bagging ring, and more specifically, a filter housing assembly for an air filter having a ring for bag-in/bag-out filter replacement.
2. Description of the Related Art
Contamination housing assemblies are used in critical processes where hazardous airborne materials must be prevented from escaping to the atmosphere. A filter is disposed in the contamination housing assembly to remove the hazardous and other materials from the air stream passing through the housing assembly. The housing assembly may be configured to include at least one filter, such as a particulate filter, a HEPA filter, and/or molecular filters for absorbing molecular contaminants.
The filters disposed in the contamination housing assembly are periodically replaced using a control barrier to protect change-out personnel from contaminants within the housing and from contaminants captured by the filters. The typical control barrier utilized is a plastic bag enclosure system such as described in U.S. Pat. No. 3,354,616, issued Nov. 28, 1967. The portion of the housing that facilitates the use of a plastic bag to remove and replace filters from a contamination housing assembly is typically known as a Bag-In/Bag-Out (BIBO) feature.
The BIBO feature consists of a bagging ring, which is generally some type of flange that extends perpendicular from the face of the containment housing around the perimeter of the opening where the filter is installed. This ring often has grooves or channels formed into it. A bag, manufactured from PVC or other suitable material has an opening containing an elastic cord or O-ring that is capable of stretching sufficiently to slide over the outside circumference of the bagging ring. The cord fits securely against the bagging ring and keeps the bag attached to the containment housing. The bag essentially forms a boundary between the contaminated interior of the containment housing and personnel performing service work on the exterior of the housing. After a filter is initially installed in the containment housing, before the system is put into beneficial operation, the bag is installed. The bag is then neatly folded and stored in the cavity created by the bagging ring. The access door is then installed to seal the opening circumscribed by the bagging ring.
In many applications, the interior of the containment housings and the filters installed in the containment housings are exposed to microorganisms, bacteria, viruses, or other contaminants that are hazardous or potentially fatal to humans. Before filters are serviced or replaced in such applications, it is common to “decontaminate” the filter and the containment housing prior to removing the access door. This decontamination is conducted by closing the bubble-tight dampers located upstream and downstream of the filter and then connecting a decontamination system to valves located on the containment system upstream and downstream of the filter. Once connected to the decontamination system, the valves are opened and a sterilization agent is circulated through the housing, in a closed loop system, at a given concentration and duration that is suitable for killing the organism on the filter and inside of the housing. There are several chemical agents that are used for decontamination including vaporized hydrogen peroxide (VHP), formaldehyde, ethylene oxide and chlorine dioxide. Decontamination is not effective on all microorganisms and bacteria. For instance, prions are not “killed” or effectively deactivated through the use of such decontamination agents. Therefore, if prions are present in a contaminated system, personnel servicing the containment system or filter are still at risk when exposed to the interior of the containment housing and filter even after the system has been decontaminated.
In those applications where organisms are not effectively eliminated or the type of organisms present in a system is of great concern in regard to human health and safety, it is essential that the bag previously described is installed prior to initial startup of the system. With the bag installed, personnel may remove the access door from the housing during servicing without direct exposure to the interior of the housing. If the bag is not installed, personnel are exposed to the interior of the housing when the access door is removed. If contaminants such as prions are present, personnel are directly exposed to the contaminant. With an increase in the number of facilities installing containment systems and a growing lack of trained and experienced personnel, the risk to human health and safety is increasing, particularly in an exhaust application where the system has been operational and contaminated with microorganisms, bacteria, viruses, or other contaminants that are harmful and potentially fatal to humans.
Thus, there is a need for a housing having a safeguard relating to the presence of a bag installed in the housing.
The center portion of the installed bag is typically rolled, folded or otherwise collapsed and stored in aperture bounded by the bagging ring while the door of the housing is closed. Upon opening the door, the center portion may unroll and drop from the housing. The dropping center portion of the bag may hit and damage equipment, hit service technicians or damage the integrity of the bag.
Thus, there is a need for a bag having means for securing its center portion when the bag is installed in a contamination housing.